The objective of the proposed research is to determine whether a teleost fish, Atlantic croaker, is a reliable model for investigating the effects of chemicals on reproductive endocrine function in female vertebrates. This will be achieved by comparing the effects of lead, benzo(a)pyren, Aroclor 1254 and clomiphene (chemicals representing four classes of reproductive toxins) on reproductive endocrine function in croaker in previously published data on their effects in mammals. The synthesis and actions of gonadal steroids as well as their conjugation and excretion will be investigated both in vivo and in vitro using modern endocrinological techniques. These techniques include radioimmunoassay, radio receptor assay, in vitro steroid biosynthesis from radioactive precursors and separation of products by HPLC and TLC, in vitro oocyte maturation bioassay. Effects of chemicals on the actions of gonadotropin will also be determined using two in vitro bioassays. Indices of reproductive impairment such as ovarian growth, oocyte maturation and ultimate hatching success will also be assessed in order to determine the signficiance of these pertubations in endocrine fucntion. The accumulation of the model compounds by ovarian tissues and oocytes will be measured to determine whether a correlation exists betweent he chemical burden in the organ and the degree of reproductive endocrine dysfunction. These studies will provide valuable new information on the sites and mechanisms of toxicant action on reproductive endocrine function in vertebrates. A long-term goal of this research is to develop this teleost model as an alternative method for assessig the effects of chemicals on endocrine and reproductive function in vertebrates. Potential advantages of using this model are (a) lower costs for animal care, (b) greater public acceptance as test organisms, (c) large amounts of ovarian tissue for in vitro testing, (d) applicability as an early-warning indicator of pollution damage to aquatic ecosystems and the potential reproductive hazards of environmental contamination to human populations.